This invention relates to a watt demand dial register having a clutch mechanism for periodically uncoupling a dial indicator from a rotatable measuring element driving in response to variations of a quantity to be measured.
Dial registers are typically used in various types of meters for indicating the consumption of different quantities to be measured. In electric energy meters, a disk and shaft assembly that is electromagnetically driven. The assembly forms a measuring element which is rotatable at the rate of consumption of electric energy. The rotations are coupled by one or more register gear trains to dial pointers indicating kilowatt demand of power usage. When measurements are to be made only during preselected time intervals, such as for only a part of each day, the dial pointers must remain uncoupled from the measuring element while it continues to rotate. A clutch mechanism is required to be provided in the register to selectively couple and uncouple the dial pointers. Many prior art register clutch mechanisms produced additional frictional drag or additional rotational torque loading on the rotatable measuring element while the clutch is uncoupled. The mechanical loading on the register gear trains cause them to wear excessively and substantially shorten the operational lifetime of the register. The substantial variations in loads on the rotatable measuring element during measuring and non-measuring times can cause it to become unstable, produce excessive wear on the disc shaft bearing and substantially reduce the operational lifetime of the measuring element.
In U.S. Pat. No. 3,406,338, issued Oct. 15, 1968, a maximum watt demand meter is disclosed including a block interval demand register having a clutch mechanism which is open briefly at the end of each demand measuring interval, which may be every fifteen, thirty or sixty minutes. A clutch driving member includes a sleeve which carries an input gear at one end and a frictional clutch surface at the other end. The driving member is uncoupled from a driven member when it is engaged by an operator member formed by a trip lever or arm member having a fork configuration. The driving member is shifted axially by the trip lever to be disengaged and uncoupled from the driven clutch member. The clutch is only opened or disengaged for two to five seconds. The additional frictional and rotational forces on the driven member due to being shifted to the open position is not applied sufficiently long to take up the backlash on the associated gear train connected to it. If the clutch mechanism were to be held open for a substantial time, as required in on and off peak or time of day demand registers, for example, the additional loading on the clutch driving member would be coupled to the gear train and/or the rotations of the measuring element.
One example of an on-peak off-peak watt demand register is described and claimed in U.S. Pat. No. 3,913,014, issued Oct. 14, 1975. The register in the aforementioned patent includes selective coupling and uncoupling with the demand measuring gear train by demeshing a pair of gears in accordance with a programmed cam surface. Misalignment of mating gears can retard the return to the mutually meshed relationship. A pusher drive and reset mechanism utilizing an additional clutch mechanism is suggested for use in the aforementioned patent in which such clutch mechanism is described in U.S. Pat. No. 2,259,314, issued Oct. 14, 1941.